Push-to-talk (PTT) devices are commonly employed by public safety personnel, air traffic controllers, emergency workers, construction site workers and others who need to be in constant and readily available voice communication. PTT, also known as press-to-transmit, is a method of communicating using half-duplex communication lines. A PTT button may be pressed to switch a device from a voice reception mode to a transmit-mode. For example, one operator may depress the PTT button on her device and speak into the device's microphone. The speech is converted into an appropriate format and transmitted to one or more other devices, where the operators of those other devices hear the first operator speak through their device's speakers. In situations where using a PTT button may not be feasible or convenient, a voice operated command may be employed to switch a device into the transmit-mode.
In high density environments where devices are within close proximity of each other, and especially in multicast situations where a transmission is received at multiple different devices, feedback may be introduced into the PTT communications. For example, when a communication device which is in a transmit-mode is within the vicinity of a receive-mode communication device, the playback from the receive-mode communication device's speaker may be received as input by the microphone of the transmit-mode device, causing acoustic feedback. Acoustic feedback may degrade voice transmission and playback, and at extreme situations, may make the devices unusable for PTT communication.
Acoustic feedback problems are typically mitigated by using acoustic echo cancellation based on digital signal processing to “remove” or attenuate certain components from the audio stream or to shift certain acoustic frequency ranges. However, these solutions are typically designed for full-duplex telephony systems and are not effective for half-duplex PTT communications. In a full-duplex system, acoustic feedback happens when the audio output of a device is fed back into the audio input of the same device. In a half-duplex system, acoustic feedback happens when the audio output of a device is fed back into the audio input of another device transmitting on the same channel. Inter-device acoustic feedback introduces unpredictable delay and jitter which significantly reduces the effectiveness of acoustic echo cancellation. Accordingly, there is a need for an improved system and method for reducing feedback in PTT communications.
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The system and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.